Michael J. Beran, Ph.D.
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September 1, 2021



Beran, M. J. (2002). Maintenance of self-imposed delay of gratifcation by four chimpanzees (Pan troglodytes) and an orangutan (Pongo pygmaeus). Journal of General Psychology, 129, 49-66.

Delay maintenance, which is the continuance over time of the choice to forgo an immediate, less preferred reward for a future, more preferred reward, was examined in four chimpanzees (Pan troglodytes) and one orangutan (Pongo pygmaeus). In the first experiment, the apes were presented with 20 chocolate pieces that were placed, one-at-a-time, into a bowl that was within their reach. The apes could consume the available chocolate pieces at any time during a trial, but no additional pieces would be given. The total length of time taken to place the 20 items into the bowl ranged from 60 s to 180 s. All five apes delayed gratification on a majority of trials until all 20 chocolate pieces were presented. Unlike in most experiments with human children using this test situation, attention by the apes to the reward was not detrimental to delay maintenance. In a second experiment with the chimpanzees only, 4 foods of differing incentive value were presented in different trials in the same manner as in Experiment 1. The chimpanzees were highly successful in obtaining all food pieces, and there was no difference in performance as a function of food type.

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